The present invention relates to a novel apparatus for accurately controlling moisture levels of aqueous surfactant compositions (e.g., personal wash or personal product compositions, detergent compositions etc.), without having to stop the process to measure water content (i.e., on-line processing). Moisture control can also be maintained in the aqueous slurry phase used in preparation of powder detergents. In one embodiment of the invention, the apparatus is useful for preparing personal wash formulations (e.g., toilet bar formulations). The toilet bar formulations may be pure soap formulations, pure synthetic surfactant formulations or formulations containing mixtures of both.
The final moisture content of an aqueous surfactant composition can be very critical. For example, the moisture content of a toilet bar composition (which is eventually processed into a material suitable for plodding and stamping) significantly effects the processing characteristics as well as the user properties of the final toilet bar product.
Thus, for example, if the toilet bar mixture has a low final moisture content, the product may not lather well, may crack too readily or may be difficult to process. Conversely, if the moisture content of the mixture is too high, processing problems may also arise (e.g., stickiness and softness).
Final moisture value of a toilet bar soap mixture is generally roughly calculated by allowing a mixer to heat the mixture to defined temperature levels for set periods of time and further calculating amounts of water that has evaporated. In U.S. Pat. No. 4,663,070 to Dobrovolny et al. moisture levels were estimated based on viscosity of the soap blend in the mixer. Although these methods are on-line methods for calculating moisture, they are not completely accurate because of raw material variations that include inaccuracies in the amounts of material charged to the mixer as well as variations in raw material quality.
Accordingly, if a way could be found to measure final moisture content directly in the mixer, this would greatly enhance the accuracy with which water content could be measured and allow applicants to more greatly control the processing, the final use properties, and the physical properties of the toilet bar or personal washing composition.
The apparatus of the invention is not limited to use in personal washing compositions however, and can be used for the preparation of any aqueous surfactant composition in which it is required or it would be useful to know moisture content without stopping production. Thus, for example, it could be used to control moisture levels for personal product compositions (e.g., shampoos), detergent compositions (i.e., laundry compositions) and fabric care compositions among others.
Soviet Union Patent 811,124 discloses a method of controlling moisture in food samples. In the apparatus used therein, however, the samples must be weighed and then compared to a standard which must also be analyzed. This is not an on-line process. Thus the process is different. Moreover, the art (i.e. food) is non-analogous.